Electrochemical Reduction of Surface Metal Oxides

This application is a continuation-in-part of, and claims priority to, U.S. patent application Ser. No. 18/077,225, filed Dec. 7, 2022, which is incorporated herein by reference.

Embodiments of the disclosure generally relate to methods for converting surface metal oxides to pure metal. In particular, embodiments of the disclosure pertain to methods for reducing metal oxides by microwave process.

Exposing pure metal materials to air can result in a thin layer of metal oxide being formed on the surface of the metal. This surface layer of metal oxide can interfere with the selectivity of subsequent processing steps and increase resistance of interconnects. Accordingly, there is a need for methods of preventing and/or cleaning metal oxides from the surface of metal materials.

While integrated processing apparatus and transportation of wafers under vacuum has decreased the need for removal of these metal oxide layers, the current preclean methods typically require a hydrogen plasma, high processing temperatures (greater than 300° C.), and/or high energy argon (Ar) sputtering. However, these processes can often damage adjacent dielectric materials (e.g., feature sidewalls) and adversely affect the selectivity of many metal deposition processes (e.g., selective tungsten deposition).

Also, current preclean methods need to be developed and/or tuned for different metal oxide materials (e.g., WOx, MoOx, CoOx, RuOx, CuOx, etc). Each different material may requires a different plasma source, different reactant gas mixtures or chemical soaks, and/or different processing conditions (e.g., temperature, pressure).

Accordingly, there is a need for universal methods of converting surface metal oxides to pure metal. Further, there is particular need for processes performed at relatively low temperatures without damaging surrounding materials.

Embodiments of the disclosure generally relate to methods for converting surface metal oxides to pure metal. In particular, embodiments of the disclosure pertain to methods for reducing metal oxides by microwave process.

In some embodiments, a method includes positioning a semiconductor structure within a processing chamber. The semiconductor structure includes an SiOlayer deposited on a substrate surface, a hardmask layer deposited over the SiOlayer, a feature formed from a low-k dielectric material deposited over a portion of the hardmask layer, and a metal layer deposited in the feature. The metal layer includes a molybdenum (Mo) layer and a molybdenum oxide layer (MoOx). The method further includes flowing a process gas into the processing chamber. The process gas includes carbon monoxide. The method further includes applying a microwave energy to the process gas to perform a redox operation on a portion of the semiconductor structure.

In some embodiments, a method includes positioning a semiconductor structure within a processing chamber. The semiconductor structure includes an SiOlayer deposited on a substrate surface, a hardmask layer deposited over the SiOlayer, a feature formed from a low-k dielectric material deposited over a portion of the hardmask layer, and a metal layer deposited in the feature. The metal layer includes a molybdenum (Mo) layer and a molybdenum oxide layer (MoOx). The method further includes flowing a process gas into the processing chamber. The process gas includes carbon monoxide. The method further comprises applying a microwave energy to the process gas to perform a redox operation on a portion of the semiconductor structure. The microwave energy is applied at a first power level that is about 1% to about 10% below a second power level. The second power level is a lowest power level that generates a plasma.

In some embodiments, a method includes positioning a semiconductor structure within a processing chamber. The semiconductor structure includes an SiOlayer deposited on a substrate surface, a hardmask layer deposited over the SiOlayer, a feature formed from a low-k dielectric material deposited over a portion of the hardmask layer, and a metal layer deposited in the feature. The metal layer includes a first layer having molybdenum (Mo) and a second layer having molybdenum oxide (MoOx). The method further includes flowing a process gas into the processing chamber. The process gas includes carbon monoxide. The method further includes applying a microwave energy to the process gas to perform a redox operation on a portion of the semiconductor structure. Greater than about 95% of the MoOx is converted to Mo.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

Before describing several exemplary embodiments of the disclosure, it is to be understood that the disclosure is not limited to the details of construction or process steps set forth in the following description. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways.

The term “about” as used herein means approximately or nearly and in the context of a numerical value or range set forth means a variation of ±15% or less, of the numerical value. For example, a value differing by ±14%, ±10%, ±5%, ±2%, ±1%, ±0.5%, or ±0.1% would satisfy the definition of “about.”

As used in this specification and the appended claims, the term “substrate” or “wafer” refers to a surface, or portion of a surface, upon which a process acts. It will also be understood by those skilled in the art that reference to a substrate can refer to only a portion of the substrate, unless the context clearly indicates otherwise. Additionally, reference to depositing on a substrate can mean both a bare substrate and a substrate with one or more films or features deposited or formed thereon.

A “substrate surface” as used herein, refers to any substrate or material surface formed on a substrate upon which film processing is performed during a fabrication process. For example, a substrate surface on which processing can be performed include materials such as silicon, silicon oxide, strained silicon, silicon on insulator (SOI), carbon doped silicon oxides, amorphous silicon, doped silicon, germanium, gallium arsenide, and any other materials such as metals, metal nitrides, metal alloys, and other conductive materials, depending on the application. Substrates include, without limitation, semiconductor wafers. Substrates may be exposed to a pretreatment process to polish, etch, reduce, oxidize, hydroxylate, anneal and/or bake the substrate surface. In addition to film processing directly on the surface of the substrate itself, in the present disclosure, any of the film processing steps disclosed may also be performed on an under-layer formed on the substrate as disclosed in more detail below, and the term “substrate surface” is intended to include such under-layer as the context indicates. Thus, for example, where a film/layer or partial film/layer has been deposited onto a substrate surface, the exposed surface of the newly deposited film/layer becomes the substrate surface.

The substrate surface may have one or more features formed therein, one or more layers formed thereon, and combinations thereof. The shape of the feature can be any suitable shape including, but not limited to, trenches, holes and vias (circular or polygonal). As used in this regard, the term “feature” refers to any intentional surface irregularity. Suitable examples of features include but are not limited to trenches, which have a top, two sidewalls and a bottom extending into the substrate, and vias which have one or more sidewall extending into the substrate to a bottom.

The term “on” indicates that there is direct contact between elements. The term “directly on” indicates that there is direct contact between elements with no intervening elements.

As used in this specification and the appended claims, the terms “precursor”, “reactant”, “reactive gas” and the like are used interchangeably to refer to any gaseous species that can react with the substrate surface.

Embodiments of the disclosure advantageously provide methods for reducing surface metal oxides at relatively low temperatures without affecting neighboring materials. Specific embodiments advantageously provide methods of reducing metal oxides which utilize a microwave process. In some embodiments, the metal oxide layer is not exposed to a plasma.

The embodiments of the disclosure are described by way of the figures, which illustrate processes, substrates and apparatus in accordance with one or more embodiments of the disclosure. The processes, schemes, and resulting substrates shown are merely illustrative of the disclosed processes, and the skilled artisan will recognize that the disclosed processes are not limited to the illustrated applications.

illustrates a schematic representation of a processing systemfor use with one or more embodiments of the disclosure. As detailed below, substrates in the processing systemmay be processed in and transferred between the various chambers without exposing the substrates to an ambient environment exterior to the processing system(for example, an atmospheric ambient environment such as may be present in a fab). For example, the substrates may be processed in and transferred between the various chambers maintained at a low pressure (for example, less than or equal to about 300 Torr) or sub-atmospheric pressure, such as a vacuum environment, without breaking the reduced relative pressure or vacuum environment among various processes performed on the substrates in the processing system. Accordingly, the processing systemmay provide for an integrated solution for some processing of substrates.

Examples of a processing system that may be suitably modified in accordance with the teachings provided include the Endura®, Producer® or Centura® integrated processing systems or other suitable processing systems commercially available from Applied Materials, Inc., located in Santa Clara, California (CA), United States of America. One may envision that other processing systems, including those from other manufacturers, may be adapted to benefit from aspects described.

is a schematic top view of the processing system(also referred to as a “processing platform”), according to embodiments described herein. The processing systemgenerally includes an equipment front-end module (EFEM)for loading substrates into the processing system, a first load lock chambercoupled to the EFEM, a transfer chambercoupled to the first load lock chamber, and a plurality of other chambers coupled to the transfer chamberas described in detail below. The EFEMgenerally includes one or more robotsthat are configured to transfer substrates from the front opening unified pods (FOUPs)to at least one of the first load lock chamberor the second load lock chamber. Proceeding counterclockwise around the transfer chamberfrom the buffer portionA of the first load lock chamber, the processing systemincludes a first dedicated degas chamber, a first pre-clean chamber, a first pass-through chamber, a second pass-through chamber, a second pre-clean chamber, a second degas chamberand the second load lock chamber. The buffer portionA of the transfer chamberincludes a first robotthat is configured to transfer substrates to each of the load lock chambers,, the degas chambers,, the pre-clean chambers,and the pass-through chambers,.

The back-end portionB of the transfer chamberincludes a second robotthat is configured to transfer substrates to each of the pass-through chambers,and the processing chambers coupled to the back-end portionB of the processing system. The processing chambers can include a first processing chamber, a second processing chamber, a third processing chamber, a fourth processing chamberand a fifth process chamber. In general, the processing chambers,,,,can include at least one of an atomic layer deposition (ALD) chamber, chemical vapor deposition (CVD) chamber, physical vapor deposition (PVD) chamber, etch chamber, degas chamber, an anneal chamber, and other type of semiconductor substrate processing chamber. In some embodiments, one or more of the processing chambers,,,,are a PVD chamber. In some examples, the pre-clean chambermay be capable of performing an etch process, the pre-clean chambermay be capable of performing a cleaning process or an annealing process, and the processing chambers,,,,may be capable of performing respective CVD or ALD deposition processes. In one example, the processing chambers,,,, ormay be a Volta™ CVD/ALD chamber, or Encore™ PVD chambers available from Applied Materials of Santa Clara, Calif.

The buffer portionA and back-end portionB of the transfer chamberand each chamber coupled to the transfer chambermay be maintained at a vacuum state. As used herein, the term “vacuum” may refer to pressures less than 760 Torr, and will typically be maintained at pressures near 10Torr (that is, ˜10Pa). However, some high-vacuum systems may operate below near 10Torr (that is, ˜10Pa). In certain embodiments, the vacuum is created using a rough pump and/or a turbomolecular pump coupled to the transfer chamberand to each of the one or more process chambers (for example, process chambers-). However, other types of vacuum pumps are also contemplated.

A system controller, such as a programmable computer, is coupled to the processing systemfor controlling one or more of the components therein. For example, the system controllermay control the operation of one or more of the processing chambers, such as processing chambers,,,,. In operation, the system controllerenables data acquisition and feedback from the respective components to coordinate processing in the processing system.

The system controllerincludes a programmable central processing unit (CPU)A, which is operable with a memoryB (for example, non-volatile memory) and support circuitsC. The support circuitsC (for example, cache, clock circuits, input/output subsystems, power supplies, etc., and combinations thereof) are conventionally coupled to the CPUA and coupled to the various components within the processing system.

In some embodiments, the CPUA is one of any form of general purpose computer processor used in an industrial setting, such as a programmable logic controller (PLC), for controlling various monitoring system component and sub-processors. The memoryB, coupled to the CPUA, is non-transitory and is typically one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk drive, hard disk, or any other form of digital storage, local or remote.

Herein, the memoryB is in the form of a computer-readable storage media containing instructions (for example, non-volatile memory), that when executed by the CPUA, facilitates the operation of the processing system. The instructions in the memoryB are in the form of a program product such as a program that implements the methods of the present disclosure (for example, middleware application, equipment software application, etc.). The program code may conform to any one of a number of different programming languages. In one example, the disclosure may be implemented as a program product stored on computer-readable storage media for use with a computer system. The program(s) of the program product define functions of the embodiments (including the methods described herein). Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (for example, read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (for example, floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the methods described herein, are embodiments of the present disclosure. The various methods disclosed herein may generally be implemented under the control of the CPUA by the CPUA executing computer instruction code stored in the memoryB (or in memory of a particular processing chamber) as, for example, a software routine. When the computer instruction code is executed by the CPUA, the CPUA controls the chambers to perform processes in accordance with the various methods.

As will be described further below, in one or more embodiments of the substrate processing sequence described herein, all of the processes are performed under vacuum within the processing system. In one example of the processing system, a remote-plasma-source (RPS) cleaning process is performed in pre-clean chamber, a precleaning process is performed in pre-clean chamber, and one or more of a deposition, an etching, and/or a thermal processing process is performed in at least one of the processing chambers,,,, and. In one example, the remote plasma (RPS) assisted process performed in pre-clean chamberis performed in a processing chamber, such as Aktiv™ Preclean (APC) chamber available from Applied Materials of Santa Clara, Calif. In another example, the processing chambers,,,, ormay be a Volta™ CVD/ALD chamber, or Encore™ PVD chambers available from Applied Materials of Santa Clara, Calif.

In another example of the processing system, a remote-plasma-source (RPS) cleaning process and a precleaning process are both performed in at least one of the pre-clean chambersand, and one or more of a deposition, an etching, and/or a thermal processing process is performed in at least one of the processing chambers,,,, and. In one example, the processing chambers,,,, ormay be a Volta™ CVD/ALD chamber, or Encore™ PVD chambers available from Applied Materials of Santa Clara, Calif.

Referring to, a cross-sectional illustration of an exemplary processing toolis shown. The processing toolmay be a processing tool suitable for any type of processing operation that utilizes microwaves. While the embodiments described in detail herein are directed to microwave processing methods, it is to be appreciated that additional processing methods (including plasma processing methods) may also be practiced on processing tool. Further, it is also to be appreciated that the PEALD methods described herein may also be performed using differing processing tools.

Generally, the processing toolincludes a chamber. In processing toolsthat are used for substrate processing, the chambermay be a vacuum chamber. A vacuum chamber may include a pump (not shown) for removing gases from the chamber to provide the desired vacuum. Additional embodiments may include a chamberthat includes one or more gas linesfor providing processing gasses into the chamberand exhaust linesfor removing byproducts from the chamber. While not shown, it is to be appreciated that the processing tool may include a showerhead or other gas distribution assembly for evenly distributing the processing gases over a substrate.

In some embodiments, the substratemay be supported on a chuck. For example, the chuckmay be any suitable chuck, such as an electrostatic chuck. The chuck may also include cooling lines and/or a heater to provide temperature control to the substrateduring processing.

The processing toolincludes one or more microwave sources. The microwave sourcemay include solid state microwave amplification circuitryand an applicator. In some embodiments, a voltage control circuitprovides an input voltage to a voltage controlled oscillatorin order to produce microwave radiation at a desired frequency that is transmitted to the solid state microwave amplification circuitryin each microwave source. After processing by the microwave amplification circuitry, the microwave radiation is transmitted to the applicator. In some embodiments, an arrayof applicatorsare coupled to the chamberand each function as an antenna for coupling the microwave radiation to the substratein the chamber.

Referring now to, a series of illustrations depicting a microwave processing toolis shown, in accordance with an embodiment. The microwave processing toolgenerates microwaves that are useful for low temperature reduction of metal oxides.

Referring now to, a cross-sectional illustration of a microwave processing tool(referred to as processing toolfor short) is shown, according to an embodiment. The processing tool may emit high-frequency electromagnetic radiation. In some embodiments, one or more of the pre-clean chambersand, or even chambers-, may include the processing tool. As used herein, “high-frequency” electromagnetic radiation includes radio frequency radiation, very-high-frequency radiation, ultra-high-frequency radiation, and microwave radiation. “High-frequency” may refer to frequencies between 0.1 MHz and 300 GHz.

Generally, embodiments include a processing toolthat includes a chamber. In processing tool, the chambermay be a vacuum chamber. A vacuum chamber may include a pump (not shown) for removing gases from the chamber to provide the desired vacuum. Additional embodiments may include a chamberthat includes one or more gas linesfor providing processing gasses into the chamberand exhaust linesfor removing byproducts from the chamber. While not shown, it is to be appreciated that gas may also be injected into the chamberthrough a source array(e.g., as a showerhead) for evenly distributing the processing gases over a substrate.

In an embodiment, the substratemay be supported on a chuck. For example, the chuckmay be any suitable chuck, such as an electrostatic chuck. The chuckmay also include cooling lines and/or a heater to provide temperature control to the substrateduring processing. Due to the modular configuration of the high-frequency emission modules described herein, embodiments allow for the processing toolto accommodate any sized substrate. For example, the substratemay be a semiconductor wafer (e.g., 200 mm, 300 mm, 450 mm, or larger). Alternative embodiments also include substratesother than semiconductor wafers. For example, embodiments may include a processing toolconfigured for processing glass substrates, (e.g., for display technologies).

According to an embodiment, the processing toolincludes a modular high-frequency emission source. The modular high-frequency emission sourcemay comprise an array of high-frequency emission modules. In an embodiment, each high-frequency emission modulemay include an oscillator module, an amplification module, and an applicator. As shown, the applicatorsare schematically shown as being integrated into the source array.

In an embodiment, the oscillator moduleand the amplification modulemay comprise electrical components that are solid state electrical components. In an embodiment, each of the plurality of oscillator modulesmay be communicatively coupled to different amplification modules. For example, each oscillator modulemay be electrically coupled to a single amplification module. In an embodiment, the plurality of oscillator modulesmay generate incoherent electromagnetic radiation. Accordingly, the electromagnetic radiation induced in the chamberwill not interact in a manner that results in an undesirable interference pattern.

In an embodiment, each oscillator modulegenerates high-frequency electromagnetic radiation that is transmitted to the amplification module. After processing by the amplification module, the electromagnetic radiation is transmitted to the applicator. In an embodiment, the applicatorseach emit electromagnetic radiation into the chamber. In some embodiments, the applicatorscouple the electromagnetic radiation to the substratein the chamber. In some embodiments, the applicatorscouple the electromagnetic radiation to the processing gasses in the chamberto provide energy thereto, without forming a plasma.

Referring now to, a schematic of a solid state high-frequency emission moduleis shown, in accordance with an embodiment. In an embodiment, the high-frequency emission modulecomprises an oscillator module. The oscillator modulemay include a voltage control circuitfor providing an input voltage to a voltage controlled oscillatorin order to produce high-frequency electromagnetic radiation at a desired frequency. The voltage controlled oscillatoris an electronic oscillator whose oscillation frequency is controlled by the input voltage. According to an embodiment, the input voltage from the voltage control circuitresults in the voltage controlled oscillatoroscillating at a desired frequency.

According to an embodiment, the electromagnetic radiation is transmitted from the voltage controlled oscillatorto an amplification module. The amplification modulemay include a driver/pre-amplifier, and a main power amplifierthat are each coupled to a power supply. According to an embodiment, the amplification modulemay operate in a pulse mode. For example, the amplification modulemay have a duty cycle between 1% and 99%. In a more particular embodiment, the amplification modulemay have a duty cycle between approximately 15% and 50%.

In an embodiment, the electromagnetic radiation may be transmitted to the thermal breakand the applicatorafter being processed by the amplification module. However, part of the power transmitted to the thermal breakmay be reflected back due to the mismatch in the output impedance. Accordingly, some embodiments include a detector modulethat allows for the level of forward powerand reflected powerto be sensed and fed back to the control circuit module. It is to be appreciated that the detector modulemay be located at one or more different locations in the system (e.g., between the circulatorand the thermal break). In an embodiment, the control circuit moduleinterprets the forward powerand the reflected power, and determines the level for the control signalthat is communicatively coupled to the oscillator moduleand the level for the control signalthat is communicatively coupled to the amplification module. In an embodiment, control signaladjusts the oscillator moduleto optimize the high-frequency radiation coupled to the amplification module. In an embodiment, control signaladjusts the amplification moduleto optimize the output power coupled to the applicatorthrough the thermal break. In an embodiment, the feedback control of the oscillator moduleand the amplification module, in addition to the tailoring of the impedance matching in the thermal break, may allow for the level of the reflected power to be less than approximately 5% of the forward power. In some embodiments, the feedback control of the oscillator moduleand the amplification modulemay allow for the level of the reflected power to be less than approximately 2% of the forward power.

Accordingly, embodiments allow for an increased percentage of the forward power to be coupled into the processing chamber, and increases the available power provided to the process gases disposed within the processing volume. Furthermore, impedance tuning using a feedback control is superior to impedance tuning in typical slot-plate antennas. In slot-plate antennas, the impedance tuning involves moving two dielectric slugs formed in the applicator. This involves mechanical motion of two separate components in the applicator, which increases the complexity of the applicator.

Referring now to, a perspective view illustration of a source arrayis shown, in accordance with an embodiment. In an embodiment, the source arraycomprises a dielectric plate. A plurality of cavitiesare disposed into a first surfaceof the dielectric plate. The cavitiesdo not pass through to a second surfaceof the dielectric plate. The source arraymay further include a plurality of dielectric resonators. Each of the dielectric resonatorsmay be in a different one of the cavities. Each of the dielectric resonatorsmay comprise a holein the axial center of the dielectric resonator.

In an embodiment, the dielectric resonatorsmay have a first width W, and the cavitiesmay have a second width W. The first width Wof the dielectric resonatoris smaller than the second width Wof the cavities. The difference in the widths provides a gap G between a sidewall of the dielectric resonatorsand a sidewall of the cavity. In the illustrated embodiment, each of the dielectric resonatorsare shown as having a uniform width W. However, it is to be appreciated that not all dielectric resonatorsof a source arrayneed to have the same dimensions.

Referring now to, a cross-sectional illustration of a processing toolthat includes an assemblyis shown, in accordance with an embodiment. In an embodiment, the processing tool comprises a chamberthat is sealed by an assembly. For example, the assemblymay rest against one or more O-ringsto provide a vacuum seal to an interior volumeof the chamber. In other embodiments, the assemblymay interface with the chamber. That is, the assemblymay be part of a lid that seals the chamber. In an embodiment, the processing toolmay comprise a plurality of processing volumes (which may be fluidically coupled together), with each processing volume having a different assembly. In an embodiment, a chuckor the like may support a substrate(e.g., wafer, workpiece, etc.). The substratemay be a distance D from the assembly. That is, the chambermay be a vacuum chamber. In an embodiment, the assemblycomprises a source arrayand a housing. The source arraymay comprise a dielectric plateand a plurality of dielectric resonatorsextending up from the dielectric plate. Cavitiesinto the dielectric platemay surround each of the dielectric resonators. Sidewalls of the cavityare separated from the sidewall of the dielectric resonatorby a gap G. The dielectric plateand the dielectric resonatorsof the source arraymay be a monolithic structure, or the dielectric plateand the dielectric resonatorsmay be discrete components.

The housinginclude ringsthat fit into the gaps G. In an embodiment, the ringsand the conductive bodyof the housingare a monolithic structure, or the conductive bodyand the ringsmay be discrete components. The housingmay having openings sized to receive the dielectric resonators. In an embodiment, monopole antennasmay extend into holes in the dielectric resonators. The monopole antennasare each electrically coupled to power sources (e.g., high-frequency emission modules).